package com.typhoon.spring_shiro.utils;

/**
 * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
 * 
 * @author tajo
 */
public class IdWorker
{
    private final static long twepoch = 1288834974657L;

    // 机器标识位数
    private final static long workerIdBits = 5L;

    // 数据中心标识位数
    private final static long datacenterIdBits = 5L;

    // 机器ID最大值
    private final static long maxWorkerId = -1L ^ ( -1L << workerIdBits );

    // 数据中心ID最大值
    private final static long maxDatacenterId = -1L ^ ( -1L << datacenterIdBits );

    // 毫秒内自增位
    private final static long sequenceBits = 12L;

    // 机器ID偏左移12位
    private final static long workerIdShift = sequenceBits;

    // 数据中心ID左移17位
    private final static long datacenterIdShift = sequenceBits + workerIdBits;

    // 时间毫秒左移22位
    private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    private final static long sequenceMask = -1L ^ ( -1L << sequenceBits );

    private static long lastTimestamp = -1L;

    private long sequence = 0L;

    private final long workerId;

    private final long datacenterId;

    public IdWorker( long workerId, long datacenterId )
    {
        if ( workerId > maxWorkerId || workerId < 0 )
        {
            throw new IllegalArgumentException( "worker Id can't be greater than " + maxWorkerId + " or less than 0" );
        }
        if ( datacenterId > maxDatacenterId || datacenterId < 0 )
        {
            throw new IllegalArgumentException( "datacenter Id can't be greater than " + maxDatacenterId + " or less than 0" );
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized long nextId()
    {
        long timestamp = timeGen();
        if ( timestamp < lastTimestamp )
        {
            try
            {
                throw new Exception( "Clock moved backwards.  Refusing to generate id for " + ( lastTimestamp - timestamp ) + " milliseconds" );
            }
            catch ( Exception e )
            {
                e.printStackTrace();
            }
        }

        if ( lastTimestamp == timestamp )
        {
            // 当前毫秒内，则+1
            sequence = ( sequence + 1 ) & sequenceMask;
            if ( sequence == 0 )
            {
                // 当前毫秒内计数满了，则等待下一秒
                timestamp = tilNextMillis( lastTimestamp );
            }
        }
        else
        {
            sequence = 0;
        }
        lastTimestamp = timestamp;
        // ID偏移组合生成最终的ID，并返回ID
        long nextId = ( ( timestamp - twepoch ) << timestampLeftShift ) | ( datacenterId << datacenterIdShift ) | ( workerId << workerIdShift ) | sequence;

        return nextId;
    }

    private long tilNextMillis( final long lastTimestamp )
    {
        long timestamp = this.timeGen();
        while ( timestamp <= lastTimestamp )
        {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    private long timeGen()
    {
        return System.currentTimeMillis();
    }

    public static void main( String[] args )
    {
        IdWorker worker2 = new IdWorker( 1, 3 );
        IdWorker worker3 = new IdWorker( 3, 3 );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker2.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
        System.out.println( worker3.nextId() );
    }

}
